The present invention relates to a rotational angle detecting device for detecting a rotational angle, a torque detecting device for detecting a torque applied to an input shaft through a torsional angle generated on a connecting shaft for connecting the input shaft and an output shaft, and a steering apparatus for an automobile comprising the torque detecting device.
In an electric power steering apparatus having such a construction that a steering auxiliary motor is driven based on a detection result of a steering torque applied to a steering wheel for steering and the rotating force of the motor is transmitted to a steering apparatus to assisting in steering, there is an advantage that an auxiliary force characteristic corresponding to a running state such as a vehicle speed or a steering frequency can be controlled more easily than a hydraulic power steering apparatus using a hydraulic actuator as a source for generating steering auxiliary force. In recent years, therefore, the coverage of the device has tended to be enlarged.
In the electric power steering apparatus described above, a torque detecting device for detecting a steering torque is required. Therefore, there has been used a torque detecting device having such a construction that an input shaft on the steering wheel side and an output shaft on the steering mechanism side of the steering shaft for connecting the steering wheel and the steering mechanism a re connected to each other through a torsion bar having a small diameter, a relative angular displacement generated in the connecting portion of both shafts is detected with the torsion of the torsion bar through the action of a steering torque and the steering torque (rotational torque) is calculated based on the detection result.
FIG. 1 is a schematic view showing an example of the construction of a torque detecting device applied to a steering apparatus for an automobile which has been proposed in Japanese Patent Application No. 2000-49912 by the present applicant. In the steering apparatus, a steering shaft 3 has such a construction that an input shaft 31 having an upper end connected to a steering wheel 30 and an output shaft 32 having a lower end connected to a pinion 33 of a steering mechanism are connected coaxially through a torsion bar 34 having a small diameter and the steering wheel 30 connects with the steering mechanism. The torque detecting device has the following construction in the vicinity of the connecting portion of the input shaft 31 and the output shaft 32.
A disk-shaped target plate 2 is externally fixed coaxially to the input shaft 31 in the vicinity of an end portion for connecting the output shaft 32, and a plurality of targets 20 (ten targets in the drawing) are parallelly disposed on the outer circumferential surface of the target plate 2. These targets 20 are protrusions formed of a magnetic material which have a partial spiral configuration inclined at almost equal angles with respect to the axial direction of the input shaft 31 to which the target plate 2 is attached as shown in the development view of FIG. 2 in which the outer circumferential surface of the target plate 2 is developed.
The same target plate 2 as that described above is also fixed externally to the output shaft 32 in the vicinity of the end portion for connecting the input shaft 31, and a plurality of targets 20 inclined at almost equal angles are matched and arranged in a circumferential direction with the targets 20 on the input shaft 31 side in the axial direction of the output shaft 32 to which the target plate 2 is attached on the outer periphery thereof.
Two sensor boxes 1a and 1b are provided on the outside of the target plates 2 to face the outer edges of the targets 20 on the outer circumferential surface periphery in the circumferential direction. The sensor boxes 1a and 1b are fixed and supported in a portion such as a housing which bears the input shaft 31 and the output shaft 32 and does not move. The sensor box 1a contains a magnetic sensor 1A opposed to the target 20 on the input shaft 31 side and a magnetic sensor 2A opposed to the target 20 on the output shaft 32 side with circumferential positions aligned accurately. Similarly, the sensor box 1b contains a magnet sensor 1B opposed to the target 20 on the input shaft 31 side and a magnetic sensor 2B opposed to the target 20 on the output shaft 32 side with circumferential positions aligned accurately.
The magnetic sensors 1A, 1B, 2A and 2B are constituted by using elements having such a property that an electric characteristic (resistance) is changed by the action of a magnetic field, for example, a magnetoresistance effect element (MR element) so that a detection signal can be varied depending on the close portions of the opposed targets 20. Detection signals V1A, V1B, V2A and V2B of the magnetic sensors 1A, 1B, 2A and 2B are given to a operating unit 4 using a microprocessor provided on the outside of the sensor boxes 1a and 1b. 
In the torque detecting device having such a construction, the targets 20 opposite to the magnetic sensors 1A, 2A, 1B and 2B are protrusions formed of a magnetic material which are arranged with predetermined inclinations in the axial direction on the outer circumferential surfaces of the input shaft 31 and the output shaft 32. Accordingly, when the input shaft 31 and the output shaft 32 rotate therearound, the magnetic sensors 1A, 2A, 1B and 2B output detection signals which are varied proportionally depending on a change in the rotational angles of the input shaft 31 and the output shaft 32 while the corresponding targets 20 pass through positions opposed thereto.
At this time, the detection signals of the magnetic sensors 1A and 1B correspond to the rotational angle of the input shaft 31 where the targets 20 opposite to the magnetic sensors 1A and 1B are provided, and the detection signals of the magnetic sensors 2A and 2B correspond to the rotational angle of the output shaft 32 where the targets 20 opposite to the magnetic sensors 2A and 2B are provided. Accordingly, the operating unit 4 can calculate the rotational angle of the input shaft 31 from the detection signals of the magnetic sensors 1A and 1B, so that the operating unit 4 and the magnetic sensors 1A and 1B operate as a rotational angle detecting device for the input shaft 31. Moreover, the operating unit 4 can calculate the rotational angle of the output shaft 32 from the detection signals of the magnetic sensors 2A and 2B, so that the operating unit 4 and the magnetic sensors 2A and 2B operate as a rotational angle detecting device for the output shaft 32.
A difference between the detection signal of the magnetic sensor 1A and that of the magnetic sensor 2A or a difference between the detection signal of the magnetic sensor 1B and that of the magnetic sensor 2B corresponds to a difference (relative angular displacement) in a rotational angle between the input shaft 31 and the output shaft 32. The relative angular displacement corresponds to a torsional angle generated on the torsion bar 34 connecting the input shaft 31 and the output shaft 32 under the action of a rotational torque applied to the input shaft 31. Accordingly, the rotational torque applied to the input shaft 31 can be calculated based on the difference in the above mentioned detection signal.
In the torque detecting device described above, the detection signals of the magnetic sensors 1A, 2A, 1B and 2B have unstable peak values because a great non-linearly change region is generated in the vicinity of both ends of the target 20 and a relatively small linearly change region is changed proportionally to a change in the rotational angles of the input shaft 31 and the output shaft 32 as shown in the waveform chart of FIG. 3, and it is difficult to calculate the rotational angle and the rotational torque, and furthermore, it is hard to correct them.
Moreover, the end of the target is fine. Therefore, when forming is to be carried out by using a metal mold, an error is made easily and the lifetime of the metal mold is shortened so that a manufacturing cost is increased.
In consideration of the above-mentioned circumstances, first to seventh aspects of the present invention have an object to provide a rotational angle detecting device in which a target is formed easily, the detection signal of detecting means has a stable peak value and a rotational angle can be calculated and corrected readily.
An eighth aspect of the present invention has an object to provide a torque detecting device using the rotational angle detecting device according to the first to seventh aspects of the present invention.
A ninth aspect of the present invention has an object to provide a steering apparatus using the torque detecting device 25 according to the eighth aspect of the present invention.
A first aspect of the present invention is directed to a rotational angle detecting device characterized by comprising: a rotating member; a target which is provided on the rotating member and whose portion to be detected is continuously changed as the rotating member rotates; and one or more detecting means for detecting the portion close to the target; wherein a displacement angle of the rotating member from the detecting means in a rotational direction is detected based on the detected portion of the target detected by the detecting means.
In the rotational angle detecting device, the target is provided on the rotating member for continuously changing a portion to be detected as the rotating member rotates, and one or more detecting means for detecting a portion close to the target and detects a displacement angle therefrom in a rotational direction of the rotating member based the detected portion.
Consequently, it is possible to realize a rotational angle detecting device capable of easily forming targets, stabilizing a peak value of a detection signal of the detecting means and readily calculating and correcting a rotational angle.
A second aspect of the present invention is directed to the rotational angle detecting device, wherein the target has a first inclining portion provided with an inclination in one direction along a circumferential surface of the rotating member and a second inclining portion provided with an inclination in the other direction along the circumferential surface of the rotating member.
In the rotational angle detecting device, the target has a first inclining portion provided with an inclination in one direction along a circumferential surface of the rotating member and a second inclining portion provided with an inclination in the other direction along the circumferential surface of the rotating member. Therefore, it is possible to realize a rotational angle detecting device capable of easily forming targets, stabilizing a peak value of a detection signal of the detecting means and readily calculating and correcting a rotational angle.
A third aspect of the present invention is directed to the rotational angle detecting device, wherein the first inclining portion and the second inclining portion have a relationship of almost line symmetry with respect to a straight line in an axial direction of the rotating member to pass through a connecting point of the both inclining portions.
In the rotational angle detecting device, the first inclining portion and the second inclining portion have a relationship of almost line symmetry with respect to a straight line in an axial direction of the rotating member to pass through a connecting point of the inclining portions. Therefore, it is possible to realize a rotational angle detecting device capable of easily forming targets, reducing a non-linear region of a detection signal which is generated in the connecting portion of the inclining portions and the end of the target, stabilizing a peak value of a detection signal of the detecting means and readily calculating and correcting a rotational angle.
A fourth aspect of the present invention is directed to the rotational angle detecting device, wherein a plurality of targets are provided continuously along the circumferential surface of the rotating member.
In the rotational angle detecting device, a plurality of targets are provided continuously along the circumferential surface of the rotating member. Therefore, it is possible to realize a rotational angle detecting device capable of easily forming targets, increasing a detection sensitivity, stabilizing a peak value of a detection signal of the detecting means and readily calculating and correcting a rotational angle.
A fifth aspect of the present invention is directed to the rotational angle detecting device, wherein the target is formed by irradiating a beam to be a heat source along the circumferential surface of the rotating member.
In the rotational angle detecting device, the target is formed by irradiating a beam to be a heat source along the circumferential surface of the rotating member. Therefore, it is possible to realize a rotational angle detecting device capable of easily forming targets, stabilizing a peak value of a detection signal of the detecting means and readily calculating and correcting a rotational angle.
A sixth aspect of the present invention is directed to the rotational angle detecting device, wherein the target outputs each standard detection signal value when the detecting means performs detection, based on a deviation of each detection signal value outputted by detecting each portion of a master target as a standard by the detecting means and the standard detection signal value to be outputted by detecting each portion by the detecting means.
In the rotational angle detecting device, the target outputs each standard detection signal value when the detecting means performs detection, based on a deviation of each detection signal value outputted by detecting each portion of a master target as a standard by the detecting means and the standard detection signal value to be outputted by detecting each portion by the detecting means.
Therefore, it is possible to realize a rotational angle detecting device capable of easily providing a target having a small non-linear region of a detection signal which is generated in the connecting portion of the inclining portions and the end portions, stabilizing a peak value of a detection signal of the detecting means and readily calculating and correcting a rotational angle. Moreover, a detection error of the detecting means can be corrected in advance during manufacture.
A seventh aspect of the present invention is directed to the rotational angle detecting device, wherein the target is magnetically discontinuous for a circumferential portion, and the detecting means is a magnetic sensor.
In the rotational angle detecting device, the target is magnetically discontinuous for a circumferential portion, and the detecting means is a magnetic sensor. Therefore, it is possible to realize a rotational angle detecting device capable of easily forming targets, readily performing handling, reducing the cost of parts stabilizing a peak value of a detection signal of the detecting means and readily calculating and correcting a rotational angle.
An eighth aspect of the present invention is directed to a torque detecting device for detecting a torque applied to an input shaft based on a torsional angle generated on a torsion bar for coaxially connecting the input shaft and an output shaft, characterized by comprising: a rotational angle detecting device according to any one of first through seventh aspect which is attached to each of the input shaft and the output shaft; means for detecting a difference between displacement angles detected by the rotational angle detecting devices; wherein a difference between the displacement angles which is detected by the detecting means is detected as the torsional angle.
In the torque detecting device, a torque applied to an input shaft is detected based on a torsional angle generated on a torsion bar for coaxially connecting the input shaft and an output shaft. The rotational angle detecting device according to any of the first through seventh aspects of the invention is attached to each of the input shaft and the output shaft, and the detecting means detects a difference between displacement angles detected by the rotational angle detecting device, and a difference between the displacement angles which is detected by the detecting means is detected as the torsional angle generated on a torsion bar.
Consequently, it is possible to realize a torque detecting device using a rotational angle detecting device capable of easily forming targets, stabilizing a peak value of a detection signal of the detecting means and readily calculating and correcting a rotational angle.
A ninth aspect of the present invention is directed to a steering apparatus characterized by comprising an input shaft connected to a steering wheel, an output shaft connected to a steering mechanism, a torsion bar for connecting the input shaft and the output shaft, and a torque detecting device according to the eighth aspect of the invention which detects a steering torque applied to the input shaft based on a torsional angle generated by the torsion bar.
In the steering apparatus, an input shaft is connected to a steering wheel, an output shaft is connected to a steering mechanism, a torsion bar connects the input shaft and the output shaft. The torque detecting device according to the eighth aspect of the present invention detects a steering torque applied to the input shaft based on a torsional angle generated by the torsion bar.
Consequently, it is possible to realize a steering apparatus comprising a torque detecting device capable of accurately detecting a steering torque and easily forming targets of a rotational angle detecting device.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.